ABSTRACT
Transport processes through the gas-liquid interfaces are of paramount importance in a number of areas of industrial engineering, such as chemical and mechanical engineering, and for geophysical and environmental systems. In such systems, gaseous pollutants may be directly exchanged between air and water in either direction across the air-water interface. Gas fluxes being transferred can be upward to the air or downward to the water depending on the substances involved. Thus, gas transfer is a two-way process involving both gas absorption, i.e. air to water, and volatilization, i.e. water to air, across an air-water interface, for a volatile or semi-volatile chemical. In the environmental fluid mechanics field, for processes at the free surfaces of terrestrial water bodies, early interest related the absorption of atmospheric oxygen in natural waters. This process is also termed as atmospheric reaeration. Since dissolved oxygen (DO) is commonly considered as the main indicator of aquatic ecosystem health, reaeration is one of the most relevant source of DO in the water bodies, whose DO level are depleted by natural causes or the discharge of organic matter (USEPA, 1985; Chapra, 1997). The volatilization of many chemicals, such as mercury, PCBs, PAHs and pesticides, has been widely recognized as an important process determining the transport, fate, and chemical loadings of these contaminants in the atmosphere and in large water bodies, such as lakes, estuaries and oceans (USEPA, 1997). Also, the assessment of volatilization rate of environmentally important compounds of low molecular weight such as benzene, chloroform, methylene chloride, and toluene from rivers and streams contaminated by spills or industrial discharges has been subject of continuing interest. Therefore the estimation of both reaeration and volatilization rate is a key issue in the application of a modeling framework of dissolved oxygen balance or of contaminant transport and fate (Chapra, 1997).
